Waves in the mHz frequency range are prominent features of the terrestrial magnetosphere. In this frequency range the waves have wavelengths comparable to the lengths of the geomagnetic field lines. The waves are then standing waves along closed field lines with endpoints in the southern and northern ionosphere. Waves play an important role in the distribution of energy in the magnetosphere and mHz waves can accelerate electrons to MeV energies and have been proposed as driving mechanism for auroral arcs. They can also be used as diagnostic tools for determining the plasma density. There are two important classes of these low frequency waves. One has large azimuthal wavelength and is usually associated with driving mechanisms outside the magnetosphere, such as the Kelvin-Helmholtz instability at the magnetopause. The other has small azimuthal wavelength and is associated with plasma instabilities inside the magnetosphere. Both types of waves are studied in this thesis with a slight emphasis on the large azimuthal wavelength waves. For the type of wave with large azimuthal wavelength there is however, a considerable debate about the driving mechanism. One recently suggested driver is coherent magnetohydrodynamic waves in the solar wind. Part of this thesis studies this experimentally and we conclude that, at least on some occasions, this driving mechanism comes into play. The Cluster satellites are used to study the morphology of the waves. We demonstrate the ability of Cluster to determine the azimuthal wave number of the waves and also how the structure along the magnetic field lines can be determined. This gives information regarding the harmonic number of the standing waves, which in turn says something about the driver of the waves. We also look at possible excitation mechanisms for the small azimuthal wavelength waves. / QC 20100707

The electrodynamic coupling between the auroral ionosphere and the magnetosphere is the main subject of this thesis. Satellite measurements of electric and magnetic fields and of charged particles are used to explore three distinct plasma boundaries, magnetically linked to the nightside auroral ionosphere. These boundaries are the inner edge of the plasma sheet (PS), and the inner and the outer edges of the plasma sheet boundary layer (PSBL). Strong ionospheric electric fields with amplitudes up to 400 mV/m may be observed in the subauroral ionosphere, in the vicinity of the ionospheric projection of the PS inner edge. Intense and dynamic auroral electric fields with local magnitudes up to 150 mV/m associated with upward ion beams and field-aligned currents are observed for the events treated here, at the inner and outer boundaries of the PSBL at an altitude of about 4-5 Earth radii, well above the acceleration region. Subauroral and auroral electric fields are the two main subjects of this thesis. Subauroral ion drifts (SAID) are associated with poleward electric fields, occurring predominantly in the premidnight region during the substorm recovery phase. The recently revealed abnormal subauroral ion drifts (ASAID) are associated with equatorward electric fields, occurring during extended periods of low auroral activity. The results indicate that the generation mechanism of SAID can neither be regarded as a pure voltage generator nor a pure current generator, but having certain characteristics of both generator types. Ionospheric feedback appears to play a major role for the development and maintenance of the SAID electric fields. The formation of ASAID is proposed to result from the proximity and interaction between different plasma boundaries of the innermost magnetosphere during extended periods of low auroral activity. The auroral electric fields observed in the upward current region at the PSBL inner and outer edges are associated with upward parallel electric fields, which partially decouple the high-altitude electric fields from the ionosphere. This is in contrast to the subauroral electric fields which are coupled. Multi-point measurements provided by the Cluster mission show that the observed electric fields are highly variable in space and time, revealing various types of acceleration processes. However, they appear to be tied to the boundary where they are originally formed. A case is  presented where they are associated with large electromagnetic energy fluxes directed upward away from the ionosphere. The interaction between the magnetosphere and ionosphere, being more pronounced at plasma boundary regions, is important for the understanding of the formation and regulation of the highly structured auroral electric fields observed in the upward current region. / QC 20100727

A detailed characterization of the proton and neutron induced radiation environment onboard Columbus and the International Space Station (ISS) has been carried out using the Geant4 Monte Carlo particle transport toolkit. Dose and dose equivalent rates, as well as penetrating particle spectra corresponding to incident trapped protons, GCR protons, SPE protons and cosmic ray albedo neutrons are presented. These results are based on detailed Geant4 geometry models of Columbus and ISS, comprising a total of about 750 and 350 geometry volumes, respectively. Additionally, the physics models of Geant4 have been validated with respect to space radiation shielding applications. Geant4 physics configurations based on the “Binary Cascade” and “Bertini Cascade” models of hadronic reactions were found to adequately model the particle interactions of the relevant space radiation fields. Other studied Geant4 models of hadronic reactions were found to be unsatisfactory for this application. Calculated trapped proton dose rates are found to be strongly dependent on ISS altitude. Dose rates for different locations inside the Columbus cabin are presented, as well as for different models of the incident space radiation flux. Dose rates resulting from incident anisotropic trapped protons are found to be lower, or equal to, those of omnidirectional models. The anisotropy induced by the asymmetric shielding distribution of Columbus/ISS is also studied. GCR proton dose rates are presented, and it is demonstrated that the presence of thick shielding may increase the dose rate. A possible problem using Geant4 for future studies of effects induced by high-energy GCR ions is discussed. The dose rate due to cosmic ray albedo neutrons is demonstrated to be negligible. The calculated trapped proton dose rates are 120 μGy/d and 79 μGy/d for solar minimum and maximum conditions, respectively. GCR dose rates are estimated based on calculated GCR proton dose rates to 161 μGy/d and 114 μGy/d, respectively. These dose rates are found to be compatible with experimental measurements. / QC 20110125

The Earth ionosphere is a highly inhomogeneous medium containing electron density irregularities of various scales, from hundreds of kilometers to tens of centimeters. Understanding the mechanisms responsible for their formation is an important task for various practical applications such as communication, navigation, and safe satellite operation. Of special interest are the decameter irregularities that are abundant at E region heights of ~ 100 120 km. These are excited when enhanced electric field and plasma drifts are setup in the ionosphere. This thesis is aimed at studying the physics of decameter irregularity formation at E region heights with a focus on the extreme conditions of very strong electric fields (plasma flows) of > 50 mV/m (1000 m/s) for which the so called Farley-Buneman (FB) plasma instability is the dominating mechanism of irregularity excitation. The relationship between the irregularity velocity and plasma drift is investigated by considering data of the SuperDARN radar located at Stokkseyri, Iclenad. The radar detects echoes from the irregularities and is thus capable of measuring their velocity. The DMSP satellites measure the plasma drifts in situ at heights of ~ 800 km, but these measurements can be projected onto E region heights at high latitudes. By comparing the radar and satellite data in one direction, we show that irregularity velocity is smaller than the plasma drift by a factor of 2 3 with the stronger difference at faster flows. This contrasts with the theoretical expectation for the velocity to be close to 400 m/s, the nominal ion-acoustic speed at electrojet heights. A two-dimensional comparison is performed by considering a subset of the observations for which the HF echo velocity showed a cosine type variation with the radar look direction. This class of echoes is consistent with predictions of recent theories of the Farley-Buneman instability, but the irregularity velocity magnitude was found to be smaller than the ion-acoustic speed with occasional occurrence of velocities as small as 100 m/s. This implies that either recent theories of the Farley-Buneman instability should be modified or that the typical height of HF echoes is typically below 100 km. Various other properties of decameter irregularities are investigated and discussed in view of the existing theories.

The Earth ionosphere is a highly inhomogeneous medium containing electron density irregularities of various scales, from hundreds of kilometers to tens of centimeters. Understanding the mechanisms responsible for their formation is an important task for various practical applications such as communication, navigation, and safe satellite operation. Of special interest are the decameter irregularities that are abundant at E region heights of ~ 100 120 km. These are excited when enhanced electric field and plasma drifts are setup in the ionosphere. This thesis is aimed at studying the physics of decameter irregularity formation at E region heights with a focus on the extreme conditions of very strong electric fields (plasma flows) of > 50 mV/m (1000 m/s) for which the so called Farley-Buneman (FB) plasma instability is the dominating mechanism of irregularity excitation. The relationship between the irregularity velocity and plasma drift is investigated by considering data of the SuperDARN radar located at Stokkseyri, Iclenad. The radar detects echoes from the irregularities and is thus capable of measuring their velocity. The DMSP satellites measure the plasma drifts in situ at heights of ~ 800 km, but these measurements can be projected onto E region heights at high latitudes. By comparing the radar and satellite data in one direction, we show that irregularity velocity is smaller than the plasma drift by a factor of 2 3 with the stronger difference at faster flows. This contrasts with the theoretical expectation for the velocity to be close to 400 m/s, the nominal ion-acoustic speed at electrojet heights. A two-dimensional comparison is performed by considering a subset of the observations for which the HF echo velocity showed a cosine type variation with the radar look direction. This class of echoes is consistent with predictions of recent theories of the Farley-Buneman instability, but the irregularity velocity magnitude was found to be smaller than the ion-acoustic speed with occasional occurrence of velocities as small as 100 m/s. This implies that either recent theories of the Farley-Buneman instability should be modified or that the typical height of HF echoes is typically below 100 km. Various other properties of decameter irregularities are investigated and discussed in view of the existing theories.

<p>Waves in the mHz frequency range are a prominent feature in the terrestrial magnetosphere. In this frequency range the waves have wavelengths comparable to the lengths of the geomagnetic field lines. The waves are then standing waves along closed field lines with endpoints in the southern and northern ionosphere. Waves play an important role in the distribution of energy in the magnetosphere and mHz waves can accelerate electrons to MeV energies and have been proposed as a driver of auroral arcs. They can also be used as a diagnostic tool for determining the plasma density. There are two important classes of these low frequency waves. One has large azimuthal wavelength and is usually associated with driving mechanisms outside the magnetosphere, such as the Kelvin-Helmholtz instability at the magnetopause. The other has small azimuthal wavelength and is associated with plasma instabilities inside the magnetosphere. Both types of waves are studied in this thesis with an emphasis on the small azimuthal wavelength waves. For the type of wave with large azimuthal wavelength there is however, a considerable debate about the driving mechanism. One recently suggested driver is coherent magnetohydrodynamic waves in the solar wind. Part of this thesis studies this experimentally and we conclude that, at least on some occasions, this driving mechanism come into play. The Cluster satellites are used to study the morphology of the waves. We demonstrate the ability of Cluster to determine the azimuthal wave number of the waves and also how the structure along the magnetic field lines can be determined. This gives information regarding the harmonic number of the standing waves, which in turn says something about the driver of the waves. We also look at possible excitation mechanisms for the small azimuthal wavelength waves.</p>

<p>A detailed characterization of the proton and neutron induced radiation environment onboard Columbus and the International Space Station (ISS) has been carried out using the Geant4 Monte Carlo particle transport toolkit. Dose and dose equivalent rates, as well as penetrating particle spectra corresponding to incident trapped protons, GCR protons, SPE protons and cosmic ray albedo neutrons are presented.</p><p>These results are based on detailed Geant4 geometry models of Columbus and ISS, comprising a total of about 750 and 350 geometry volumes, respectively. Additionally, the physics models of Geant4 have been validated with respect to space radiation shielding applications. Geant4 physics configurations based on the “Binary Cascade” and “Bertini Cascade” models of hadronic reactions were found to adequately model the particle interactions of the relevant space radiation fields. Other studied Geant4 models of hadronic reactions were found to be unsatisfactory for this application.</p><p>Calculated trapped proton dose rates are found to be strongly dependent on ISS altitude. Dose rates for different locations inside the Columbus cabin are presented, as well as for different models of the incident space radiation flux. Dose rates resulting from incident anisotropic trapped protons are found to be lower, or equal to, those of omnidirectional models. The anisotropy induced by the asymmetric shielding distribution of Columbus/ISS is also studied. GCR proton dose rates are presented, and it is demonstrated that the presence of thick shielding may increase the dose rate. A possible problem using Geant4 for future studies of effects induced by high-energy GCR ions is discussed. The dose rate due to cosmic ray albedo neutrons is demonstrated to be negligible.</p><p>The calculated trapped proton dose rates are 120 μGy/d and 79 μGy/d for solar minimum and maximum conditions, respectively. GCR dose rates are estimated based on calculated GCR proton dose rates to 161 μGy/d and 114 μGy/d, respectively. These dose rates are found to be compatible with experimental measurements.</p>

<p>Ground-based and in-situ observations of the aurora demonstrate an extreme richness in fine structure, with spatial scales down to tens of metres and time variations occurring on a fraction of a second. To further our understanding of the aurora, it is esssential to understand the mechanisms responsible for the small-scale structuring, since this is an intrinsic property of the auroral plasma. Still many questions about dynamics and structuring of aurora on small scales remain unanswered. In this thesis the low-light optical instrument ASK (Auroral Structure and Kinetics) is used to image small-scale structures in the aurora at very high spatial and temporal resolution. ASK is a multi-spectral instrument, imaging the aurora in three selected emission lines simultaneously. This provides information on the energy of the precipitating electrons. The SIF (Spectrographic Imaging Facility) instrument has been used in conjunction with ASK, to give a more complete picture of the spectral characteristics of the aurora, and to determine the contamination of the emission lines by other emissions. Data from ASK and SIF is used to study the relation between the morphology and dynamics of small-scale structures in the aurora and the energy of the precipitating electrons. By comparing electron density profiles provided by EISCAT (European Incoherent SCATter) measurements with modeling results, information on characteristic energy and energy flux of the precipitating electrons can be obtained. One of the ASK channels is imaging a metastable O+ emission, which has a lifetime of 5 s. By tracing the afterglow in this channel optically a direct measure of the E × B drift and thus of the local ionospheric electric fields is provided.</p>

This thesis deals with heating of outowing oxygen ions at high altitude above the polar cap using data from the Cluster spacecraft. oInospheric plasma may flow up from the ionosphere but at velocities which are low enough that the ions are still gravitationally bound. For the ions to overcome gravity, further acceleration is needed. The cusp/polar cap is an important source of outowing oxygen ions. In the cusp/polar cap, transverse heating is more common than eld-aligned acceleration through a magnetic eld-aligned electric eld. It is thus believed that transverse heating of ions is important for ion outow and one of the probable explanations for transverse heating is wave-particle interaction. A general conclusion from our work on high altitude oxygen ion energization is that ion energization and outow occur in the high altitude cusp and mantle. The particles are often heated perpendicularly to the geomagnetic eld and resonant heating at the gyrofrequency is most of the time intense enough to explain the observed O+ energies measured in the high altitude (8 { 15 Earth radii, RE ) cusp/mantle region of the terrestrial magnetosphere. The observed average waves can explain the observed average O+ energies. At lower altitude only a few percent of the observed spectral density around the oxygen gyrofrequency needs to be in resonance with the ions to obtain the measured O+ energies. A difference as compared to low altitude measurements is that we must assume that almost all wave activity is due to waves which can interact with the ions, and of these we assume 50 % to be left-hand polarized. We also have shown a clear correlation between temperature and wave intensity at the gyrofrequency at each measurement point. We have described the average wave intensity and corresponding velocity diffusion oeffcients as a function of altitude in a format convenient for modelers. Furthermore we have shown that the wave activity observed in this high altitude region is consistent with Alfven waves, and inconsistent with static structures drifting past the spacecraft. We have also shown how large the variability of the observed spectral densities is, and how sporadic the waves typically are. Based on three cases we have found that the regions with enhanced wave activity and increased ion temperature are typically many ion gyro radii in perpendicular extent.

During geomagnetic storms, terawatts of power in the million mile-per-hour solar wind pierce the Earth’s magnetosphere. Geomagnetic storms and substorms create transverse magnetic waves known as Alfvén waves. In the auroral acceleration region, Alfvén waves accelerate electrons up to one-tenth the speed of light via wave-particle interactions. These inertial Alfvén wave (IAW) accelerated electrons are imbued with sub-100 meter structure perpendicular to geomagnetic field B. The IAW electric field parallel to B accelerates electrons up to about 10 keV along B. The IAW dispersion relation quantifies the precipitating electron striation observed with high-speed cameras as spatiotemporally dynamic fine structured aurora. A network of tightly synchronized tomographic auroral observatories using model based iterative reconstruction (MBIR) techniques were developed in this dissertation. The TRANSCAR electron penetration model creates a basis set of monoenergetic electron beam eigenprofiles of auroral volume emission rate for the given location and ionospheric conditions. Each eigenprofile consists of nearly 200 broadband line spectra modulated by atmospheric attenuation, bandstop filter and imager quantum efficiency. The L-BFGS-B minimization routine combined with sub-pixel registered electron multiplying CCD video stream at order 10 ms cadence yields estimates of electron differential number flux at the top of the ionosphere. Our automatic data curation algorithm reduces one terabyte/camera/day into accurate MBIR-processed estimates of IAW-driven electron precipitation microstructure. This computer vision structured auroral discrimination algorithm was developed using a multiscale dual-camera system observing a 175 km and 14 km swath of sky simultaneously. This collective behavior algorithm exploits the “swarm” behavior of aurora, detectable even as video SNR approaches zero. A modified version of the algorithm is applied to topside ionospheric radar at Mars and broadcast FM passive radar. The fusion of data from coherent radar backscatter and optical data at order 10 ms cadence confirms and further quantifies the relation of strong Langmuir turbulence and streaming plasma upflows in the ionosphere with the finest spatiotemporal auroral dynamics associated with IAW acceleration. The software programs developed in this dissertation solve the century-old problem of automatically discriminating finely structured aurora from other forms and pushes the observational wave-particle science frontiers forward.